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[Bug ports/2749] powerpc32 does not build --without-fp


------- Additional Comments From joseph at codesourcery dot com  2006-09-15 20:07 -------
Subject: Re:  powerpc32 does not build --without-fp

On Fri, 15 Sep 2006, sjmunroe at us dot ibm dot com wrote:

> sequence we will need explicitely clear the high order 16 bits of V_f[3]. But
> this is not a glibc issue and should not delay the acceptance of soft-fp fixes.

It is a glibc issue since the correct place for the fused multiply add 
implementation is in soft-fp (it is not PowerPC-specific, but is 
generically relevant to any user of soft-fp) and the master copy of 
soft-fp is in glibc.  In any case, the double rounding is incorrect.

> >I think the bulk of the fmsub implementation should go in a macro in 
> >op-common.h, that could be used to implement the standard fma and fmaf 
> >library functions.
> 
> First, lets keep it simple and get long double working. Then since this is you
> proposal, are you voluteering to implement it ;-)

Not at present.  My suggestion is that the code (more or less as you have 
it) should go in a macro in op-common.h rather than in a PowerPC-specific 
file.  That's essentially a matter of moving the code.  And bugs should be 
kept open for the known problems, such as double rounding and the generic 
brokenness of fma/fmaf/fmal in glibc (instantiated for the various 
implementations present).  (The generic brokenness is Debian bug 372544, I 
don't think there's a glibc Bugzilla entry.  It so happens that on soft-fp 
PowerPC, there would be an easy fix for fmaf and fma with the macro added 
to op-common.h: use the soft-fp fma support.)



-- 


http://sourceware.org/bugzilla/show_bug.cgi?id=2749

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